On Thu, Mar 11, 2021 at 4:13 PM Maximilian Luz <luzmaximilian@xxxxxxxxx> wrote: > > On 3/11/21 7:51 PM, Nathan Chancellor wrote: > > On Thu, Mar 11, 2021 at 02:39:03PM +0100, Maximilian Luz wrote: > >> On 3/11/21 2:06 PM, kernel test robot wrote: > >>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master > >>> head: 98546348153dee5f8ced572fd6c4690461d20f51 > >>> commit: 797e78564634275ed4fe6b3f586c4b96eb1d86bc [1430/3917] platform/surface: aggregator_registry: Add base device hub > >>> config: arm64-randconfig-r026-20210311 (attached as .config) > >>> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 574a9dabc63ba1e7a04c08d4bde2eacd61b44ce1) > >>> reproduce (this is a W=1 build): > >>> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > >>> chmod +x ~/bin/make.cross > >>> # install arm64 cross compiling tool for clang build > >>> # apt-get install binutils-aarch64-linux-gnu > >>> # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=797e78564634275ed4fe6b3f586c4b96eb1d86bc > >>> git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git > >>> git fetch --no-tags linux-next master > >>> git checkout 797e78564634275ed4fe6b3f586c4b96eb1d86bc > >>> # save the attached .config to linux build tree > >>> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm64 > >>> > >>> If you fix the issue, kindly add following tag as appropriate > >>> Reported-by: kernel test robot <lkp@xxxxxxxxx> > >>> > >>> All warnings (new ones prefixed by >>): > >>> > >>> In file included from drivers/platform/surface/surface_aggregator_registry.c:12: > >>> In file included from include/linux/acpi.h:35: > >>> In file included from include/acpi/acpi_io.h:7: > >>> In file included from arch/arm64/include/asm/acpi.h:12: > >>> include/linux/efi.h:1093:34: warning: passing 1-byte aligned argument to 4-byte aligned parameter 2 of 'get_var' may result in an unaligned pointer access [-Walign-mismatch] > >>> status = get_var(L"SecureBoot", &EFI_GLOBAL_VARIABLE_GUID, NULL, &size, > >>> ^ > >>> include/linux/efi.h:1101:24: warning: passing 1-byte aligned argument to 4-byte aligned parameter 2 of 'get_var' may result in an unaligned pointer access [-Walign-mismatch] > >>> get_var(L"SetupMode", &EFI_GLOBAL_VARIABLE_GUID, NULL, &size, &setupmode); > >>> ^ > >>>>> drivers/platform/surface/surface_aggregator_registry.c:398:25: warning: implicit conversion from 'int' to '__u8' (aka 'unsigned char') changes value from 65535 to 255 [-Wconstant-conversion] > >>> { SSAM_VDEV(HUB, 0x02, SSAM_ANY_IID, 0x00) }, > >>> ~ ^~~~~~~~~~~~ > >> > >> This is a false positive: > >> > >>> include/linux/surface_aggregator/device.h:71:23: note: expanded from macro 'SSAM_ANY_IID' > >>> #define SSAM_ANY_IID 0xffff > >>> ^~~~~~ > >> > >> Here, clang complains that the input is SSAM_ANY_ID. That is a special > >> value which has special considerations below. The SSAM_DEVICE() and > >> thus SSAM_VDEV() macros are intended to only allow either __u8 or > >> SSAM_ANY_ID as input in this place. > >> > >>> include/linux/surface_aggregator/device.h:126:63: note: expanded from macro 'SSAM_VDEV' > >>> SSAM_DEVICE(SSAM_DOMAIN_VIRTUAL, SSAM_VIRTUAL_TC_##cat, tid, iid, fun) > >>> ^~~ > >>> include/linux/surface_aggregator/device.h:102:41: note: expanded from macro 'SSAM_DEVICE' > >>> .instance = ((iid) != SSAM_ANY_IID) ? (iid) : 0, \ > >>> ^~~ > >> > >> Here is the special handling for SSAM_ANY_ID. So there is an implicit > >> conversion from iid, which may be __u8, to int (i.e. the type of > >> SSAM_ANY_ID), but there is at no point any implicit conversion of > >> SSAM_ANY_ID to __u8, as clang alleges. > > > > Looks like we are getting bit by https://llvm.org/pr38789 here (also > > tracked at https://github.com/ClangBuiltLinux/linux/issues/92). > > Thanks for the links! Looks like this is the same issue. > > >> Is there any way to silence this warning in particular without > >> suppressing it (e.g. by explicit casting) when users of this macro > >> _actually_ input any non-u8 and non-SSAM_ANY_ID value as iid, > >> leading to an _actual_ implicit value-changing cast? > > > > This has been worked around once before, commit b27aca2e555f ("soc: > > rockchip: work around clang warning"). I am not sure of another way to > > silence the warning in specific instances like you described aside from > > just fixing clang (which is obviously the correct solution) so that we > > will get real warnings. > > > > Unfortunately, the patch that is linked in the LLVM PR above does not > > appear to fix this instance. > > So what's the way forward here? Ignore this warning for now and wait for > the clang team to fix it or find a workaround? I think we should fix this on the Clang side; having your additional test case will help us refine the initial approach. Not the highest priority for us as this was found via randconfig; if it was something that showed up for defconfigs for every arch that would help us reprioritize but at the moment we have a lot of higher priority work. Either way, I appreciate the effort looking into this 0day bot warning! > > The best workaround I can come up with is setting the match_flags > parameter directly as macro argument, which would be a bit more verbose > and feel slightly less clean, but would do the trick. > > Also note that any changes to those macros would have to be synchronized > with a couple of patches which are still out to non-pdx86 trees, so if > we're working around this it's best to do this as soon as possible. > Specifically talking to Hans here, as those patches all have a > dependency on stuff that's only in the pdx86 tree right now. I.e. > getting the workaround in before setting up a tag for those dependencies > would simplify things. > > Regards, > Max > > > Cheers, > > Nathan > > > >> I believe GCC does get this right and only emits a warning if a > >> non-u8 _and_ non-SSAM_ANY_ID value is input. > >> > >> Regards, > >> Max > >> > >>> 3 warnings generated. > >>> > >>> > >>> vim +398 drivers/platform/surface/surface_aggregator_registry.c > >>> > >>> 396 > >>> 397 static const struct ssam_device_id ssam_base_hub_match[] = { > >>> > 398 { SSAM_VDEV(HUB, 0x02, SSAM_ANY_IID, 0x00) }, > >>> 399 { }, > >>> 400 }; > >>> 401 > >>> > >>> --- > >>> 0-DAY CI Kernel Test Service, Intel Corporation > >>> https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx > >>> > >> > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/7db15c91-db37-69a4-84b7-6f58cca2ee1b%40gmail.com. -- Thanks, ~Nick Desaulniers
